Information storage and retrieval devices, such as magnetic and MO hard drive devices utilized in computer devices are comprised of a magnetic or MO hard disk recording/storage medium mounted on a spindle, which is driven by a motor to effect high speed rotation of the disk. A read/write transducer (“head”) maintained in close proximity to the surface of the rotating disk, reads or writes data on the disk. The read/write head is separated from the disk surface by an air bearing created by the high speed rotation of the disk. The read/write head “flies” on the air bearing at a very close separation distance (“flying height”) from the disk surface, i.e., on the order of microinches. The closer the read/write head is to the disk surface, the more information may be written to and read from the disk. Thus, it is desirable for the read/write head to “fly” as close as possible to the surface of the disk.
Recording media in the form of magnetic disks typically comprise a non-magnetic substrate such as of Al or an Al-based alloy, a NiP layer plated on the substrate, polished and then textured, an underlayer, e.g., of Cr or NiP deposited on the NiP plated layer, a thin film of a magnetic recording material (typically a Co-based alloy), a protective overcoat layer formed on the magnetic film, and a lubricant topcoat layer on the protective overcoat layer.
Magnetic disk manufacturing specifications typically require that asperities, protrusions, and depressions on the surface of the disk are smaller than a preselected size. The precision with which the read/write head flies over the disk surface requires that care is taken during the manufacturing processing to assure that there are no protrusions or asperities on the disk surface that may interfere with operation of the read/write head. For example, a protrusion on the surface of the disk that contacts the read/write head may damage the head and/or the disk.
Accordingly, during manufacture of magnetic or MO disks, tests are performed with “media certifiers” using, e.g., “glide heads”, to ensure that there are no defects, such as asperities, voids, projections, or contaminants present on the disk surface that might interfere with operation of the read/write head. Accurate testing of disks for such defects assures that the disk manufacturer does not unnecessarily reject good quality disks or pass on poor quality disks that may later fail in operation.
A typical certification process for hard disks involves mounting each disk individually on a spindle, which is rotated at a high speed while a burnishing head is moved across the surface to remove loose debris and condition the disk surface, followed by moving a glide head across the disk surface to check for asperities and defects. Conventionally, the burnishing head is designed as a flying head which passes over the disk surface to be burnished at a very small spacing which may even be less than the normal spacing between the disk surface and the read/write head.
The escalating requirements for high areal recording density magnetic media dictate media with ultra-smooth surfaces and ultra-thin protective overcoat layers for minimizing transducer head/disk surface separation distances, i.e., reduced flying heights approaching a near-contact situation. However, as the transducer head/disk interface of magnetic hard drives approach the near-contact regime, the number of thermal asperities (TA's) detected by the read/write transducer heads rapidly increase to an unmanageable level. These TA's, which result from a strong interaction from the flying transducer head and a defect on the disk surface, not only cause the recording tracks to be unusable for data recording, but also degrade the magnetic heads and potentially cause failure of the entire disk drive. The disadvantageous interaction resulting in TA formation can result from contact or non-contact situations, as long as they induce a sudden change in the head/media spacing. Hence, it is imperative that reducing media defects is key for ensuring good reliability of magnetic hard drives.
One of the most important processes for reducing media defects is the burnishing process. As indicated above, the objective of the burnishing is to remove the loose/soft particles and asperities from the media surface and to condition the surface. However, the continuing drive for thinner protective overcoat layers for better recording performance demands a delicate burnishing. Burnishing too aggressively will scratch the disks, and burnishing too gently will not create a flyable surface. In addition, the deteriorating wear and scratch resistance of the media surface due to the ultra-thin overcoat layer renders the disk surface more prone to particle embedding.
Conventional burnishing heads typically include burnishing surfaces comprised of a plurality of waffle- or elliptically-shaped discrete projections or pads distributed over the entire air-bearing burnishing surface. FIG. 1 is a plan view of the burnishing surface of a typical elliptical pad burnishing head. Due to their small size and discrete nature, pads configured in such waffle or elliptically-shaped manner cannot efficiently compress incoming air at the leading edge, resulting in poor flying stability and large head-to-head variation in the fly height. In either instance, it is virtually impossible to fine-tune the aggressiveness of the burnishing process and maintain a consistent/stable burnishing performance.
FIG. 2 is a plan view of the burnishing surface of a more recent burnishing head design of “straight-rail” type affording superior flying stability and improved fly height control vis-à-vis the waffle- or elliptically-shaped type head such as illustrated in FIG. 1. However, burnishing heads of the type shown in FIG. 2 disadvantageously lack aggressive, or sandpaper-type burnishing action and good particle rejection.
In view of the foregoing, there exists a clear need for improved burnishing head designs for use with current high performance magnetic or MO disk media which provide optimized burnishing performance with a sufficient degree of burnishing.
The present invention, therefore, addresses and solves the above-described problems, drawbacks, and disadvantages associated with the conventional burnishing heads and methodology utilized for the manufacture of high performance magnetic and MO recording media in disk form, while maintaining full compatibility with all aspects of automated disk manufacture.